The invention as directed to a differential amplifier having controllable power sources.
A differential amplifier of this type is described in the book "Design of MOS VLSI Circuits for Telecommunications" by Y. Tsividis and P. Antognetti, Prentice Hall, N.J. (1985), pages 129 through 136, C.F. particulary FIG. 5.4. Two field effect transistors connected parallel to a power source and serving as controllable power sources are thereby influenced via current-mirror circuits by currents flowing in parallel voltage arms. When a fixed voltage value is exceeded by an input signal superimposed on a gate bias, one field effect transistor supplies an auxiliary current intensifying the quiescent current of the current source. The current-mirroring circuits are fashioned such that the low quiescent current is greatly boosted by the signal-dependent appearance of the auxiliary currents. Good driver properties given a simultaneous reduction of the dissipated power of the differential amplifier are thus achieved.
A disadvantage of this known amplifier, however, is that instabilities which often lead to a distortion of the output signal occur in the control circuits. Then control circuits are formed of parallel circuit branches, of current-mirroring circuits, of controllable current sources and of a further circuit branch. This instability particularly occurs when an input signal has steeply rising and decaying signal edges, for example a square-wave voltage.